1) Field of the Invention
The present invention relates to an optical information reading apparatus designed to read information codes such as bar codes.
2) Description of the Related Art
This type of conventional optical information reading apparatus (bar code reader) is made by accommodating, in a case, an illumination optical system including a plurality of LEDs and illumination lenses located in front thereof, and a light-receiving optical system including image formation lenses and light receiving sensors. The illumination optical system emits illumination light with a horizontally elongated configuration through a read opening onto an object of reading (object to be read) such as bar-code printed paper (label), and the light-receiving optical system receives the reflected light from the object of reading to read the bar codes.
In this case, so far, as the illumination lens there has commonly been employed a semicylindrical lens having an output portion formed into a cylindrical plane. On the other hand, in an appearance inspection apparatus equipped with a line sensor, it is considered to uniform the illumination light through the employment of a lenticular lens as the illumination lens (for example, Japanese Patent Laid-Open 2002-55060).
For example, as FIGS. 11A and 11B shows, a lenticular lens 1 mentioned above has, at its output plane side, a large number of convex lenses 1a formed into a continuous tier configuration so that incident light from an LED 2 emerges in a state diffused in horizontal directions (read width directions). However, this lenticular lens 1 has inflection points 1b between convex lens tiers 1a, and light does not emerge at the inflection point 1b portions, which creates a problem in that the uselessness occurs in light quantity and difficulty is experienced in uniforming the illumination light.
In addition, in the case of the appearance inspection apparatus disclosed in the aforesaid patent document, the distance between the illumination optical system and the object is made constant and, hence, there is no need to take the difference between the illumination optical axis and the image formation optical axis into consideration. On the other hand, in the case of a bar-code reader in which the distance between an illumination optical system and an object of reading can vary, there is a need to project the illumination light properly (without shifting vertically) onto a read position over the entire read depth range. This requires reducing the difference between the illumination optical axis and the image formation optical axis to the utmost.